1. Field of the Invention
This invention relates to conduit systems having a frangible connector, and more particularly to automatic sealing mechanisms for blocking the outward flow of fluid from the conduit when the connector is broken.
2. Description of the Prior Art
It is often important to prevent leaks of flammable or noxious fluids from a conduit system after the conduit has been ruptured. For example, fuel spillage from an aircraft fuel line after a crash can result in an explosion or severe fire. In order to control such spillage, frangible connectors have been developed with the object of controlling the location in a fuel line at which a break will take place, and then providing a mechanism to seal off the spillage of fuel at the frangible connector as quickly as possible.
The fuel line or other conduit is typically divided into two sections which are joined together by the frangible connector. The connector has a relatively weak linkage holding it together so that, under the stress of a crash or other accident a break will occur at the connector before anywhere else in the conduit. A valve is provided in the conduit sections on either one or both sides of the connector to stop the spillage of fluid when the connector is broken. It is important that the valves be fast operating, reliable and, for aerospace applications, as small and lightweight as possible.
One type of valve assembly for a frangible connector is disclosed in U.S. Pat. No. 4,090,524 issued May 23, 1978 to Allread et al., entitled "Frangible Valved Fitting", and assigned to Aeroquip Corporation. In this patent a flapper valve is provided in the conduit section on each side of the connector. The flapper valves employ valve discs which are pivotally connected at one end and normally held along the inside of the conduit wall. The flaps are retained in this position by a spring loaded sleeve which moves when the connector is broken, releasing the flaps and allowing them to pivot down to seal off their respective conduit sections. While this mechanism provides adequate fluid sealing when it operates properly, the sliding sleeve release mechanism has a considerable area which is subject to corrosion or silting, causing the mechanism to bind up and prevent the flaps from releasing. Furthermore, since the release mechanism occupies a considerable volume along the side of the conduit, a larger overall conduit must be used in order to achieve the same fuel carrying capacity. This in turn results in a greater conduit weight, which is quite detrimental in aerospace applications. Also, because the flaps, sliding sleeve and associated springs are all in the fluid flow path, the valve mechanism presents an appreciable resistance to fluid flow, and there are numerous cavities which can ice up if any water is present in the fuel and prevent the valves from operating properly. Finally, although the flaps are urged closed by a spring mechanism, the device does not have a positive locking mechanism to assure that they remain closed.
Another type of frangible connector valving system is supplied by the Spectrum Company under the trademark BALVAC. In this device a pair of spring loaded ball valves are rotated to a closed position when a frangible connector between the valves is broken. The ball valves and their associated control mechanisms greatly increase the overall diameter of the conduit without increasing its fluid carrying capacity, thus resulting in an unnecessary increase in weight. Furthermore, because the device relies on closely fitted sliding surfaces which extend over large areas, it is subject to binding up and failing to release properly. As in the Aeroquip patent, it is possible for a significant amount of fuel to leak out between the time the connector breaks and the valves are actually closed.
Another disadvantage of the prior art devices is that they generally have a link pin or ball which falls out when the connector is broken. It is possible for the pin or ball to become lodged in the valve mechanism, preventing a proper closure.